Everything is crap, unless you get into a chamber. But that is faaar too expensive for your average joe. Those electronic ones are terrible as well, fluctuates like crazy.
Best bet, get someone at the gym WHO KNOWS WHAT HE OR SHE IS DOING, and use calipers, with equations. at least 5 skinfold measurements. But please, get a PT who knows their stuff. Half of these people at Virgin's or the like don't have a clue.
Seriously though, don't waste your money on those. Get simple calipers that are sturdy, as in well built. Not the R200 plastic ones. Then try and teach someone. The internet has a lot of videos that you can use, and just do it time and time and time again.